IDENTIFICATION OF ADDITIONAL GENES REQUIRED FOR O-ANTIGEN BIOSYNTHESIS IN VIBRIO-CHOLERAE O1

The cloning and expression of the genes encoding the Vibrio cholerae O 1 lipopolysaccharide O antigen in a heterologous host have been descri bed previously (P. A. Manning, M. W. Heuzenroeder, J. Yeadon, D.I. Lea vesley, P. R. Reeves, and D. Rowley, Infect. Immun. 53:272-277, 1986), It was thus assumed that all the genes required for O-antigen express ion were located on a 20-kb SacI restriction fragment, We present evid ence for a number of other as yet undescribed genes that are essential for O-antigen biosynthesis in V. cholerae O1 and that these genes are somehow complemented in Escherichia coli K-12. The two genes termed V ibrio cholerae rfbV and rfbU are transcribed in the opposite orientati on from the rest of the rfb operon, whereas the galE dehydratase and r fbP (Salmonella enterica) homologs, designated ORF35x7 and rfbW, respe ctively, are transcribed in the same orientation. The evidence present ed here, using chromosomal insertion mutants, clearly shows that the t hree genes now designated rfbV, rfbU, and rfbW appear to be accessory rfb genes and are essential for O-antigen biosynthesis in V. cholerae but that ORF35x7 is not.